1. Field of the Invention
This invention relates generally to a television receiver controlled by a micro-computer and, more particularly, to an apparatus which is controlled by the micro-computer to provide backup data to the television receiver when a power failure occurs.
2. Description of the Prior Art
The alternating current power typically supplied to homes by public utility companies frequently encounters interruptions. In some instances, the power failures can last for an appreciable period of time, such as when they are caused by a storm or the like, however, in most cases such power failures are essentially instantaneous and are terminated within a second or less. Such power failures or brief outages may be caused by generator switch overs or network changes within the power grid, and brief power outages can also be caused in the home by rapid increases in load, such as when the motor of a refrigerator or air conditioner unit is suddenly switched on.
As modern television receivers become to rely more and more on digital data techniques and the associated storage of the data digital, to both tune the channel and to control picture quality and the like these power outages become quite serious, because all the operating data can be lost when the power goes down.
To accommodate these power outages, it has been proposed to provide some sort of backup, whereby the data used in a micro-computer, for example, to control the television receiver would not be lost upon the occurrence of a power outage. Generally, in a digitally controlled television receiver, a standby power source is provided to keep power on the micro-computer at all times, and this usually involves feeding a DC voltage derived from the AC line voltage to the micro-computer. Another approach to dealing with such power outages in a digitally controlled television receiver is to provide a nonvolatile memory connected to the micro-computer so that when the power source for the television is turned off, the channel selection data, sound volume data, and the like, which are typically stored in the random access memory portion of the micro-computer, may be transferred to the nonvolatile memory for storage. This data is stored therein even in the face of a power outage.
A reset circuit is also generally employed in cooperation with a standby power source so that when a power failure occurs, the central processing unit of the micro-computer is reset by the reset circuit.
Another feature of a digitally controlled television receiver typically involves time display and another problem occurs in displaying such time once a power failure occurs. Usually the timing data is stored in the random access memory and is refreshed or updated every minute and, thus, in the case of a power outage the appropriate clock data in the nonvolatile memory would have to be refreshed every minute. As is well known, however, such nonvolatile memories usually involve some sort of magnetic elements, such as a bubble memory, which can generally only be accessed about 100,000 times in its lifetime. This is perfectly adequate to accommodate the number of times a television receiver is turned on and off during its lifetime, which on the average is about seven years, however, if the nonvolatile memory were to be used for time display data storage the clock data would have to be rewritten every minute and the nonvolatile memory would quickly wear out. To accommodate this, it is typically known to back up the power source of the micro-computer by a special, large value condenser or a capacitor bank to prevent the time display data in the random access memory of the micro-computer from being erased when a power failure occurs.
Thus, the two known approaches to providing backup to a digital television receiver during a power outage involve an increase in the manufacturing cost of the television receiver.